A class of polymers known as polyimides has become known for its combination of good heat stability and high upper use temperatures, as measured by glass transition temperature. A particularly useful type of such polyimides is known as polyimidesiloxanes.
Because of their combination of properties, polyimidesiloxanes have been used in electronic applications, particularly in microelectronic components in the computer industry.
Because most of the previously known polyimidesiloxanes are insoluble or difficultly soluble in solvents, when used in the microelectronics industry, there is a great need for polyimidesiloxanes having improved solubility characteristics, as well as a better balance of heat resistance and upper use temperature.
The chemistry for making polyimides has been well-known since about 1960. A structurally simple polyimide can be prepared by reacting a diamine with a dianhydride. ##STR1##
The first step, or the polycondensation reaction, generates polyamide acids which are hydrolytically unstable even at room temperature. The second step, or the imidization reaction, produces the stable polyimides desired for various applications.
Polyimidesiloxanes can be prepared by reactions employing siloxane diamines or siloxane dianhydrides with organic comonomers. Polyimidesiloxanes can also be prepared from siloxane diamines and siloxane dianhydrides without an organic comonomer.
The first polyimidesiloxane was prepared by reacting pyromellitic dianhydride (PMDA) with 1,3-bis-(aminopropyl)-1,1,3,3-tetramethyl disiloxane in 1966 (see V. H. Kuckertz, Macromol. Chem. 98, 1966, pp. 101-108). This polyimidesiloxane is a crystalline material and cannot be cast into flexible films from solvent. Polyimidesiloxanes derived from reactions of benzophenone tetracarboxylic dianhydride (BTDA) and .alpha.,w-diamino organo-polysiloxanes were disclosed by General Electric in 1967 in U.S. Pat. No. 3,325,450. Polyimidesiloxanes containing an .alpha.,w-diamino organo-polysiloxane and a diether dianhydride (DEDA) have also been disclosed in U.S. Pat. No. 3,847,867.
All these BTDA and DEDA containing polyimidesiloxanes are amorphous materials. They have a glass transition temperature of no more than 100.degree. C. and, therefore, have very limited upper use temperatures, despite the excellent thermal stability of these polymers up to about 200.degree. C.
Polyimidesiloxanes containing both organic and siloxane monomers have been reported for PMDA containing copolymers (see Japan Kokai Tokkyo Koho 83/7473 and 83/13631); for BTDA containing copolymers (U.S. Pat. Nos. 3,553,282 and 4,404,350) and for diether dianhydride containing copolymers (U.S. Pat. No. 3,847,867). These PMDA containing polyimidesiloxanes are not soluble in any solvent. The BTDA containing polyimidesiloxanes are only soluble in high boiling or toxic solvents such as 1-methyl-2-pyrrolidinone, commonly known as N-methyl pyrrolidone (NMP), phenol or cresol, and the like. The diether dianhydride containing polyimidesiloxane, in addition, are also soluble in chlorinated solvents such as dichlorobenzene and dichloromethane. Since these phenol and chlorinated compounds are both corrosive and highly toxic, the polyimidesiloxanes have limited application in coating applications, especially in heat sensitive electronic devices. This is also due to the fact that a NMP soluble polyimidesiloxane normally has to be heated to 350.degree. C. for at least half an hour to remove all the residual solvent in a film having a micron-thickness film.
Only a few polyimidesiloxanes are soluble, even in high boiling and relatively toxic solvents, such as 1-methyl-2-pyrrolidinone (NMP), despite the fact that most of their polyamide acids are soluble. The usage of polyamide acids in coating applications has many drawbacks. First, a subsequent imidization reaction on substrates produces water. Therefore, it can only be used in very thin film coatings and where void-free property is not critical to performance. Second, the removal of high boiling, polar solvents, such as NMP, requires temperatures as high as 350.degree. C. for about 30 minutes even for films of a micron thickness. This drying process is not only energy intensive, but also unacceptable to some heat sensitive electronic devices or substrates. In addition, the polyamide acids solution has to be stored at refrigeration temperature (&lt;4.degree. C.) and it still has a very short shelf life (about 3 months). Finally, only the fully imidized polyimidesiloxanes are thermally stable for melt processing such as extrusion and injection molding. A soluble polyimidesiloxane can be fully imidized at temperatures of about 160.degree. to 170.degree. C. in a solvent, whereas imidization for insoluble polyimidesiloxanes in the solid state may require temperatures 50.degree. C. above their glass transition temperatures which can be as high as 200 to 250.degree. C. Shaping not fully imidized polyimidesiloxanes by the melt processing method produces voids in the products and often is not desirable.
U.S. Pat. No. 4,290,936 describes preparation of a polyimide by reacting a biphenyl tetracarboxylic acid and an aromatic diamine ingredient containing at least 50 percent of diamino-diphenyl ether in the presence of a phenol or halogenated phenolic compound. Additional diacids including benzophenonetetracarboxylic acids can also be employed. Siloxanes are not disclosed so that polyimidesiloxanes are not produced.
U.S. Pat. No. 4,520,075 describes a diglyme soluble polyimidesiloxane which is based on biphenyl tetracarboxylic dianhydride and where the polyimidesiloxane is partially imidized. The corresponding polyamic acid and fully imidized products are insoluble. The polyimidesiloxane precursors, when used in coating applications, have to be imidized and solvent removed at temperatures as high as 350.degree. C. or 400.degree. C. for 30 minutes. The usage of high temperatures limited their applications in heat sensitive semiconductor devices, as well as hybrid circuitry. In addition, these precursors are hydrolytically unstable at room temperatures and have only limited shelf life even at 4.degree. C. refrigeration temperature for about 3 months. Furthermore, these precursors during imidization produce water or bubbles in coatings when the film thickness is over a few micron meters (.gtoreq.20 .mu.m). The polyimidesiloxane precursors are not useful in thin film applications. The diaminosiloxane is used in an amount of 1 to 4 mole percent of the total diamino compound. Normal usage is at least about 15 mole percent of the siloxane component based on the total diamino components up to as high as 60 mole percent.
U.S. Pat. No. 4,634,760 is directed to polyimides based on biphenyl tetracarboxylic dianhydride and a second anhydride which may be a benzophenone tetracarboxylic dianhydride; an oxydiphthalic anhydride, or various other dianhydrides disclosed at column 1, line 60 to column 3, line 5 of the patent. The patent discloses the use of various diamines including 1,3-bis(3-aminopropyl) tetramethyldisiloxane, but there is no disclosure of making diglyme soluble polyimidesiloxanes.
Some diether dianhydride containing polyimidesiloxanes, such as disclosed in U.S. Pat. Nos. 4,586,997 and 4,670,497, are soluble in diglyme (T.sub.b =162.degree. C.) and may be sparingly soluble in tetrahydrofuran (T.sub.b =60.degree. C.); but none of these polyimidesiloxanes are soluble in solvents such as methyl ethyl ketone (T.sub.b =80.degree. C.) which is one of the most used solvents in the coating industries. However, all these polyimidesiloxanes have relative low glass transition temperatures (below about 125.degree. C. to 150.degree. C.) and limited thermal stability (350.degree. C./0.5 hour with retention of film flexibility and integrity). Thermally stable polyimidesiloxanes which are soluble in non-toxic and low boiling solvents such as diglyme or methyl ethyl ketone, are not readily available from these diether dianhydrides.
U.S. Pat. No. 4,395,527 to Berger discloses a large number of various components as useful in manufacturing polyimidesiloxanes. Both BPDA and BTDA are disclosed in this patent as useful dianhydrides, but other investigators such as the patentees of U.S. Pat. Nos. 4,520,075 and 4,634,760, have shown that the use of BPDA and BTDA individually does not lead to polyimidesiloxanes that are soluble in diglyme. Moreover, the tolylene diamine used in the present invention is not even disclosed in the cited patent.
U.S. Pat. Nos. 4,586,997 and 4,670,497 teach the utility of making polyimidesiloxanes based on diether dianhydrides, diamines and .alpha.,w- diaminosiloxanes. The use of benzophenone tetracarboxylic acid dianhydride (BTDA) is disclosed, but the illustrative examples show that polyimides based on BTDA are not soluble in diglyme. Cross-linked polymers are also disclosed.
My copending application Ser. No. 032,722, filed Mar. 31, 1987, now U.S. Pat. No. 4,770,555, discloses that fully imidized polyimidesiloxanes made from oxydiphthalic anhydrides are soluble in solvents such as diglyme, tetrahydrofuran and methyl ethyl ketone.
My copending application Ser. No. 153,898, filed on even date herewith, discloses that substantially fully imidized polyimidesiloxanes made from a bis(dicarboxyphenyl)hexafluoropropene dianhydride and mixtures with other dianhydrides are soluble in solvents such as diglyme, tetrahydrofuran and methyl ethyl ketone.
One of the objects of the present invention is to develop a fully imidized polyimidesiloxane which is soluble in low boiling, non-polar and non-toxic solvent such as diglyme. Another object of the present invention is to develop the desirable polyimidesiloxanes based on less expensive and commercially available organic monomers. Another object of the present invention is to develop less expensive polyimidesiloxane which can be quickly scaled-up into commercially available, large scale production. Another object of the present invention is to develop less expensive polyimidesiloxanes which can be used in price sensitive applications or in favorable competitive performance/cost positions in cable jacket, as well as 3D molded wire board applications and where high volume and low price are essential.
Another object of the invention is to provide fully imidized polyimidesiloxanes which are soluble not only in high boiling solvents, such as NMP, but also in low boiling, low toxic, less polar solvents such as diglyme or tetrahydrofuran (THF). A further object of the invention is to provide polyimidesiloxanes that have a good balance of heat resistance and high upper use temperatures, as measured by glass transition temperatures.
Another object of this invention is to produce curable and cross-linked polyimidesiloxanes.